1. Field of the Invention
The present invention relates to an apparatus for delivering a compressed air foam. More particularly, the present invention relates to an apparatus which allows for proportionate and precise amounts of fluid and a foaming agent surfactant to be mixed and compressed with air thereby producing foam, and where the amounts of fluid, foaming agent, air and other variables may be independently varied so as to result in the generation of a preselected consistency of foam.
2. Background Art
Compressed air foam delivery systems are commonly used for fire fighting applications. These systems are known in the art as "water expansion pumping systems" (WEPS) and "compressed air foam systems" (CAFS). Typically, these systems will include a water pump device, a device for injecting a foaming agent surfactant, and an air compression device. Foam is generated by mixing the water and the foaming agent surfactant together to create a foam solution and then agitating the mixture with compressed air. The site of actual foam generation varies among systems, but generally occurs in a hose or discharge device, or in a specially designed delivery nozzle.
There are various distinct types of foam recognized for fire fighting applications, each of which vary in their concentrations of water, air and foaming agent surfactant. These classes of foam each demonstrate different characteristics, including drainage rate, electrical conductivity, and degree of wetness or dryness. The characteristics of a foam therefore have an effect on both its ability to prevent or suppress fire and on fire fighter safety during generation and use.
Other factors will also dictate the quality and consistency of the foam generated, including the temperature of the water, the temperature of the foaming agent surfactant (or surfactant), the outside or ambient air temperature, the type of surfactant used, and the type of water used (e.g., salt water is a better foaming agent than non-salt water, depending on the surfactant).
As stated, most foam fire extinguishing systems currently in use produce foam within an unrolled fire hose accompanying such systems. The problem with such an arrangement is that a need for a fire extinguishing foam cannot be met until the fire hose is first unrolled and then the foam is subsequently produced within the hose, the process of which can be a time consuming affair. As time is of the essence in fire fighting situations, this problem is particularly acute.
Another substantial drawback of currently available compressed air foam generation systems is that they are unable to quickly alter the type of foam that is generated, based either upon the type of surfactant used and/or the aforementioned external variables. Often, especially in fire fighting applications, a specific application will require that a particular type of foam be generated. For instance, in fire fighting, certain classes of foam may only be used for chemical fires, while others are more suitable for structural fires. Thus, prior art compressed air foam generation systems are typically designed for a specific purpose, and consequently will generate only foam suitable for that, and only that, specific application. These prior art systems make it difficult, if not impossible, to alter the type of foam that is generated, especially on a "real-time" basis. Systems of this type are thus not suitable for those applications that require, or benefit from, the selective generation of different types of foams.
An additional disadvantage of prior art foam generation systems is that they are unable to quickly respond to changing external factors. For instance, air temperature and humidity, the type of fire to be extinguished, the type of surfactant available, or the type of water that is available will rarely be constant. Thus, foam quality will vary unless the system provides for a method of compensating for these variables, a feature heretofore unavailable in foam delivery systems.
Additionally, the pressure at which the compressor delivers the air foam is also dependent on a variety of factors. Hose length, hose diameter and the inclination of the hose--uphill, level or downhill--are all factors affecting delivery pressure requirements. At the same time, although delivery pressure may vary, foam quality must remain constant. Again, prior art systems are lacking in that they are unable to respond quickly to these changing variables and simultaneously deliver a foam of a particular and consistent quality. Thus, they operate effectively only under specific and non-varying conditions.